Automatic slack adjuster



Aug. 30, 1932. a. L. SMITH AUTOMATIC SLACK ADJUSTER Filed Jan. 10. 1930 ffi (Ittorneg 40 'tance of movement Patented Aug. 30, 1932 PATENT OFFICE U UNITED STATES GEORGE I4. SMITH, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO UNITED scrnprns onmmnon COMPANY, POBA'IION on VIRGINIA OF WASHINGTON, DISTRICT OF COLUMBIA, A (301B.-

AUTOMATIC SLACK ADJUSTER Application filed January 10, 1930. Serial no. 419,902.

My invention relates to automatic slack V adjusters for vehicle brakes and particularly to the type shown and described in my co pending application serially numbered 362,-

Particularly it is the purpose of my present invention to provide an improved construction for automatically increasing the,

over all length of an internal expanding full 1 wrap brake band as the brake lining wears and thus in turn to maintain the movement of the brake applying device substantially uniform for proper brake application, regardless of wear of the brake lining.

My invention. when two brakes are equipped therewith and connected by the torque operated braking effect equalizing mechanism of the type described and claimed is extended; the operation ofsaid device being automatically accomplished by mechanism included therein and operated to eifect the desired extensionduring release of the brake following a brake application wherein the elements of the brake applying device have moved a distance in excess of a predetermined amount; said operating mechanism of the extension device also including means to positively lock the same against any operative movement so long as the disdevice during brake application is withln predetermined limits, to thereby provide against the extension device being jarred out of adjustment by the vibration of an associated vehicle during travel of the latter.

' appended claims,

of the brake applying In the drawing chosen to illustrate my invention, the scope whereof is set forth in the Figure l'is a side elevation of an internal expanding brake having my invention incorporated, the brake being shown released;

Figure 2, an enlarged View of a fragment of Figure 1 showing the extension device partly in section and with the brake applied under wear conditions requiring brake applying movement of the brake applying de vice beyond a predetermined extent;

"Figure 3, a plan view of Figure 2; and

Figure 4, a section on the line H of Figure -2 with the brake released.

In the drawing I have shown my invention incorporated in an internal expanding brake which embodies a drum A Withinwhich is a full wrap expanding braking member 10 having side flangeslO' and the usual-lining 10 for braking engagement with the drum A. Mounted on the inner face of the member 10 is an inwardly directed thrust bracket 11, while an anchor 12 located between the ends of the member 10 is fixed to a nonrotating part of the brake, in the present instance the backing plate 13. To increase the effective length of the braking member 10 and thereby compensate for wear of the brake lining 10 I introduce between the thrust bracket 11 and anchor 12 my automatic slack adjuster which is shown as including a body 14, an adjusting screw 15, an adjusting sleeve 16 and an operating lever 17. The cylindrical shaped end 18 of the body 14 is bored out to snugly and rotatably receive the sleeve 16. I

Said sleeve 16 1s threaded and takes the screw 15, and has fixedly associated with the end thereof adjacent the bracket 11 a twelve tooth ratchet 19. The outer end of the screw 15 r v is slotted to straddle the flange 20 of the thrust bracket 11 and said flange is recessed as shown to prevent the screw from sliding oil the flange.

At one side of the sleeve 16 a slot 21 is cut in the body 14 and the lever 17 operates in this slot. One end of said lever is hooked over the inner end 22 of the cylindrical portion 18 of the body 14 and its other end is connected to a spring 23, which latter is anchored to the braking member 10 and constantly tends to pivot the lever 17 in a counter-clockwise direction (Figure 2) and also constantly tendsto pull said lever laterally toward the ratchet 19 as clearly shown by the direction of the spring axis in F igure 3.

The brake member 10 is expanded by a lever 27 pivoted at 28 tothe body 14, said lever also engaging pivotally the end 29 of an arm 30 rigidly secured to the opposite end of the braking member 10. The lever 27 is pivotally connected to a link 31 and the latter is to be connected in any suitable manner with a brakepedal or lever not shown. The pivotal connection between lever 27 and link 31 is in the form of a pin 32 which is extended sufliciently at one end to be positioned under the adjacent end of the lever 17.

In Figure 4 I have shown the lever 17 in section in the position it occupies when the brake is fully released and in which position it fits snugly between the side 25 of slot 21 and the side 2G.of the adjacent ratchet tooth of the ratchet 19 and whereby the sleeve 16 is normally held by the lever 17 against rotation in either direction. hen the brake is applied by a movement of the brake applying means in excess of a predetermined amount the lever 17 is rotated down to the dotted osi- .tion shown in Fig. 4 by the pressure 0 pin 32 on the end 33 and is swung to the right underv the next ratchet tooth by the action of the spring 23 as heretofore referred to.

In Figures 2 and 3 the parts are shown in the positions they would occupy when the brake is applied under wear conditions requiring movement of the lever 27 beyond a predetermined amount and-during such application or any normal application of the brake when the drum A is rotating inresponse to forward movement of an associated vehicle a gap 34occurs between the anchor 12 and body 14 and the thrust of the braking member 10 comes on anchor 12 as shown by the arrow 35. Figure 2 also discloses that the pin 32 has operated lever 17 by )ivoting it in a clockwise direction, so that it has. moved down and to the side as shown in dotted lines in Figure 4 and has picked up the tooth 36 on ratchet 19.

With the status shown in Figures 2 and 3 existing it will be apparent that as the brake is released the pin 32 will move from the full line position to the dotted line position 37. -During this movement the gap 34 closes and the spring 23 operates to return the lever 17 to the full line position in Figure 4, thereby rotating the ratchet 19 and its associated sleeve 16 the distance of one tooth, thus causmake positive and proper contact with the brake drum before the pin 32 has operated the lever 17 sufiiciently to cause said lever to pick up the next tooth of ratchet 19.

To permit free movement of the body 14 along the braking member as the screw 15 is traversed out I provide on the body 14 a foot 38 to rest against the member and force it outwardly when the brake is applied, but without interfering with the slight angular movement of body 14 with respect to the brakment of the screw 15. The side flanges .10 of the braking member also act as guides for the body 14 and prevent any lateral movement of said body. It will also be noted that the thrust of the brake when resisting backward movement of the vehicle will beimparted to the anchor 12 by the end 40 of body 14 and from that through screw 15 and the a thrust bracket 11 to the brake member 10. In

such case the gap 34 would appear on the left side of anchor 12.

It will be noted that the upward movement of link 31 beyond a certain amount causes the ratchet lever 17 to pick up a new tooth on the ratchet 19, but that the turning of sleeve 16 to extend the screw 15 does not take place until brake is released and the pressure on the various parts is relieved, and further noted that the only interval when sleeve 16 is not locked against turning is when lever 17 is in the position shown in dotted lines in Fig. 4 and this is at a time when the brake is applied and the parts under pressureto prevent any rotative movement of said sleeve 16.

As soonas the brake is released the spring 23 immediately acts to rotate the sleeve to a locked position again.

It will be further noted that the body 14 of the extensible compression device is in contact through foot 38 with the inner face of the band 10 and along which baud face it is adapted to be automatically extended as heretofore described. This contact of "the body 14 with the inner face of the band 10 is an important feature of my invention. By this construction and arrangement the body '14 will, during brake application, be heated up rapidly by the band and expand with the latter, so that the take-up action will not work too fast as the band follows the heat produced expanding action of the drum.

Were it not for this substantially uniform heating up of the band and the compression ing member caused by the rectilinearmoveand accordingly slower in cooling than the drum, aminterval would occur when the brakes would be inclined to drag.

lVhile I have illustrated and described In invention as incorporated with a braking member of the full wrap internal expanding type, it will be apparent that the same is also applicable to other types of braking members without in any manner departing" from the spirit thereof and I have accordingly claimed my invention with such intent and scope.

I claim:

1. In a brake, a braking member, an extensible device through which braking force is transmitted to the braking member, means for applying braking force to the braking member through said device, said last named means including a lever pivoted to the device, a member movable in one direction by brake applying movement of said lever, spring means for moving said member in the opposite direction during the following brake release, and means operated by the latter movement of the member to extend said device when said first movement is of predetermined extent.

2. In a brake, a brake member, brake applying means, and an automatically extensible compression device operatively connected with the brake applying means, said device including a body, a rotatable ratchet and an operating lever for the latter positioned when the brake is released to lock the ratchet against rotation in one direction by engagement with a ratchet tooth and against rotation in the opposite direction by simultaneous engagement of opposite portions of the lever with one side of the next tooth of the ratchet and the body respectively.

3. In a brake, a braking member, a thrust member carried by the brake, an extensible device one end of which bears against the thrust member, means for applying braking force to the braking member through said device and thrust member, said last named means including a lever pivoted to the device, a second lever on said device movable in one direction by brake applying mov'ei'nent of the first lever, a spring operating to move said second lever in the opposite direction during the following brake release and also constantly urging the extensible device against the thrust member through said second lever, and means operated by the latter movement of the second lever to extend said device when the first movement of the second lever is of predetermined extent.

4. In a brake, a brake member, brake applying means,a brake adjusting device operable by a predetermined amount of brake applying movement of the brake applying means and having two movements of adjustment, and means positively locking said d e-' vice against either adjusting movement durincluding a body, arotatable sleeve carried by the body, a non-rotatable screw on which the sleeve is threaded, a oircumscribing ratchet fixed to the sleeve, a lever carried by the body and operable by the brake applying means during brake application, and means operable upon predetermined brake applying movement of the brake applying means to cause said lever to pick up an advance tooth of the ratchet and rotate the sleeve as the brake is released, said lever cooperating with said ratchet when the brake is fully released to lock the sleeve against rotation in either direction.

In testimony whereof I hereunto afiix my signature.

GEORGE L. SMITH. 

